Products are often manufactured in a continuous web format for economic reasons and to obtain processing efficiencies. When it is desirable to treat these webs with wet chemistries, i.e. for methods such as plating or coating, the web material often passes through a liquid processing tank. Continuous web processing with wet chemistry can create material handling issues as well as finished product quality issues.
A conventionally practiced electrodeposition method for continuous webs is generally shown in FIG. 1. The method includes holding a web 10 in a vertical orientation and passing it through slots 12 located on opposing ends of a liquid processing tank 14. The web 10 travels in direction 16. Idler or contact rolls 18 provide an electrical charge to the web 10. Liquid processing tank 14 contains a process solution 19 containing a component to be deposited on the web 10. Anode screens, not shown, inside the liquid processing tank 14 complete an electrical circuit causing the desired component in the process solution 19 to be deposited on the web 10. The size of the liquid processing tank 14 and the speed of the web through the liquid processing tank 14 are generally designed to achieve the desired residence time necessary to complete the processing of the web 10. However, the established length of the liquid processing tank 14 severely limits the ability to adjust residence time for different web applications through the same system, especially in a multi-step process where the ratio of residence times cannot be adjusted independently. Additionally, since it is desired that the slots 12 be wider than the thickness of the web 10, some amount of the process solution 19 escapes the liquid processing tank 14 through the slots 12 requiring a capture system. This flow of process solution 19 from the liquid processing tank 14 may cause aeration of the process solution 19 which can adversely affect the electrodeposition process and the quality of the finished web 10. Additionally, weir flows lead to situations where the residence times between the upper portion and lower portion of the web can vary resulting in cross web uniformity differences.
Web handling processes similar to the one described in FIG. 1 are often used to apply coating to delicate webs. Delicate webs are generally considered webs that are fragile either due to the thinness of the substrate or due to a lack of structural integrity caused by holes or other discontinuities in the web. Additionally, wet chemistry processing can create situations where conventional webs become fragile and thus should be treated in the same manner as delicate webs. For delicate webs, the tensions on the free span of the web may cause the material to bow or form wrinkles. In the case of electrodeposition, this will cause a non-uniform distance between the web and the anode screen resulting in poor uniformity of the deposition thickness. These wrinkles may also introduce varying stresses into the web which may exceed the critical yield stress of the web.
Horizontal processing of webs generally requires threading the web around rollers in an open top cavity liquid processing tank. The liquid processing tank is then filled with the process solution. The rollers may introduce damage, such as stretching, tears, or scratches, to the web as it is dragged over the rollers.
It would be desirable to process webs more efficiently without adversely affecting the quality of the web. It would also be desirable to process a web in a horizontal manner without concern for damage to the web caused by contact or drag over rollers. When the web of interest is delicate either due to the thinness of the substrate or a lack of structural integrity caused by holes or other discontinuities, it would be desirable to process the web at low tension to minimize residual stress in the finished web.